Delamination resistance test

Davies, P. and Moore, D.R. (1990). Glass/nylon-6.6 composites Delamination resistance testing. Composites Sci. Technol. 38, 211-227,... 

Brunner AJ, Blackman BRK, Davies P. A status report on delamination resistance testing of polymer-matrix composites. Eng Fract Mech 2008 75 2779-94. http // dx.doi.org/10.1016/j.engfracmech.2007.03.012. 

Exploratory tests with a higher loading rate of 5mm/min (maximum allowed by ISO 15024) were conducted on two SO.5/0.5 and one S2/2 specimen in order to check for indications of loading rate effects. In Fig. 6, the dashed lines show the apparent delamination resistance curves of specimens tested at a loading speed of 5mm/min, the full lines the resistance curves of the specimens tested at 2mm/min. The S2/2 specimens are represented by filled circles,... 

Fracmre mechanics tests that quantify the delamination resistance of FRP composites determine the rate of change in strain energy per unit area of delamination (i.e. the... 

Mode I cyclic compression—compression tests on CFRP-impacted CFRP plates have been performed by Katerelos et al. [38]. The analysis relies on nondestructive testing (ultrasonic C-scan) and modelling for quantification of delamination resistance. In mode II tests, there is a choice between test parameters yielding no shear reversal or... 

The literature published on fracture mechanics testing of FRPs in the last 40 years comprises a large database on delamination resistance or fracture toughness of different types of FRPs. An early review [51] compiled the data available at that time. Selected data from quasi-static mode I and mode II tests on FRPs were compared by O Brien [52], and quasi-static mode I test data from carbon—fibre epoxy and poly-ether-ether-ketone (PEEK) by Brunner [53]. Mechanical properties of FRP composites are compiled in the Composite Materials Handbook version F (2002) [9—11], but this does not comprise fracture mechanics data. Hence, there is no comprehensive and up-to-date database on the available data or literature. 

Trakas and Kortschot [76] used carbon fibre epoxy (AS4/3501-6) specimens modified with Teflon edge delaminations in a study comparing unidirectional and 0°/90° and 90°/90° interfaces under mode 1, mode 11 and mode HI loading. Delamination resistance decreased for all modes when going from unidirectional to cross-ply and 90°/90°. The tests were complemented with scanning electron microscopy of the fracture surfaces, but they did not yield a direct quantitative correlation with the measured values of Gc- It was noted that Gc could be used as a material property for design as long as the layup (ply orientation) and mode of fracmre corresponded to those in the intended use. 

Figure 8.11 Delamination resistance of symmetric cross-ply carbon fibre—epoxy (IM7/977-2) under quasi-static mode I loading, average initiation (init), average propagation (prop) and maximum prop values (averages from two to five laboratories and standard deviations) for testing from a starter crack thin-film insert and from a mode I precrack.

Tranj-laminar fracture of composites with a certain amount of fibres in the throughthickness direction will lead to fibre breaking with significant effects on delamination resistance (see e.g. Refs [24,37] for details). Woven fibre mats, 3D fibre performs or additional 3D reinforcement (pins and stitching) of FRP composites with fibres ahgned in one plane (see e.g. Refs [84,85]) have been developed and can be tested for their fracture mechanics properties. The typical approach for testing these is to apply a standard test method developed for unidirectionally reinforced FRP composites and to assess the difference in delamination resistance compared to the standard laminate. So far, that approach has yielded (nominal) numbers, but their interpretation is not... 

Figure 8.15 Dependence of the delamination resistance under quasi-static mode I loading for carbon-fibre-reinforced epoxy (IM7/977-2) on test temperature (after sufficient conditioning) for two laminate thicknesses [113] with increasing temperatures, the delamination resistance is increasing.

In some specimens, irradiation was followed by annealing. DMTA indicated some changes in transition temperature for a certain irradiation dose range, but less for others which correlated with changes in delamination resistance. The experiments discussed in the literature noted in this section all indicate a complex interaction between irradiation and temperature which would have to be taken into account in irradiation test development. Effects on composites from the space environment (irradiation with particles and electromagnetic waves, temperature variation etc.) wUl be considered in the new Composite Materials Handbook (version G, 2012 ff. [12]). For space applications, the impacts of micrometeorites and of space debris, for example from other spacecraft [124], will also contribute to damage of FRP composites and hence to ageing. 

The question of whether delamination resistance can be quantitatively characterized using existing standard test procedures or whether modified or new standard procedures have to be developed also applies to other types of FRP composites. 

Currently available data indicate that 3D reinforcements typically result in high values of Gc compared with the unidirectional laminate made from the same fibre and matrix. Whether the high delamination resistance of 3D FRP laminates does represent material values or apparent values, for example depending on specific test and specimen parameters, is still debated (see e.g. Ref. [92]). More generally, the applicability of linear elastic fracture mechanics to through-thickness reinforced FRP composites is questionable [98]. 

Brunner AJ, Stelzer S, Pinter G, Terrasi GP. Mode II fatigue delamination resistance of advanced fiber-reinforced polymer-matrix laminates towards the development of a standardized test procedure. Int J Fatigue 2013 50 57-62. http //dx.doi.org/10.1016/ j.ijfatigue.2012.02.021. 

Some investigations [105-107] on micron-.size particle-filled composites demonstrated that fracture toughness is dramatically influenced by the particle shape, size, volimie fraction, and particle/matrix interfacial strength. Brunner et al. [108] reviewed the development of fracture mechanics test methods in determination of fracture toughness and delamination resistance of fiber-reinforced polymer composites. 

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